I. Field of the Invention
The present invention relates to a method of manufacturing a phosphor screen of a cathode ray tube.
II. Description of the Prior Art
A phosphor screen having red, blue and green phosphors regularly arranged (in a predetermined pattern) is arranged on the inner surface of the faceplate of a cathode ray tube, e.g., a color picture tube.
A slurry method as disclosed in Japanese Patent Publication No. 47-38054 is known as a method of manufacturing such a phosphor screen. According to this method, a phosphor slurry containing a photoresist is coated on the entire inner surface of the faceplate. The blue phosphor is exposed through a shadow mask and developed, and then, the green phosphor is exposed and developed. Finally, the red phosphor is exposed and developed.
The slurry method has the advantage of being easily mass-produced.
A powder coating method having various advantages over the slurry method has recently been developed. As disclosed in Japanese Patent Publication No. 48-14498, in the powder coating method, a photosensitive resin which can be imparted with a predetermined stickiness upon radiation and does not contain phosphor particles is coated on the inner surface of a faceplate. The coated resin is exposed through a shadow mask to form a particle-receptive adhesive surface of a predetermined pattern, and phosphor particles are allowed to attach to the particle-receptive adhesive surface. The slurry method described above has various problems including non-precise patterning due to light scattering by phosphor particles, and especially, large phosphor particles during exposure, difficult patterning of a fine pitch for high-precision patterning, degradation of phosphor characteristics depending on the photosensitive resin used, and limitation of the type of phosphors which can be used due to the problem of gelation of phosphors with the photosensitive resin. In contrast, the powder coating method is free from such problems associated with the slurry method. In addition, the powder coating method has various advantages. For example, the process is easy, and the use of water or an organic solvent in the developing step may not be necessary depending on the type of photosensitive resin used.
As a method of allowing phosphor particles to attach to a particle-receptive adhesive surface in the powder coating method, the dusting method for dispersing powder particles in the air and blowing the dispersing particles at high speed by a spray is known. However, in the dusting method, since the particles are passed through the nozzle of the spray gun at high speed, the particles produce friction and the light-emitting intensity of the phosphor particles may be lowered. Another method is disclosed in U.S. Pat. No. 4,469,766. In this method, as shown in FIG. 1, phosphor particles 3 are charged onto the inner surface of a faceplate 1 having a particle-receptive adhesive surface of a predetermined pattern thereon. The faceplate 1 is inclined along the X-X' or Y-Y' direction to allow the phosphor particles to slide on the faceplate inner surface, thereby allowing the particles to attach to the patterned adhesive surface.
In the above method, the adhering amount of phosphor particles can be kept substantially uniform. However, when microscopically observed, irregular streak patterns in the coating are easily formed and degrade the quality of the phosphor screen. This can be considered attributable to the phosphor particles sliding in a zigzag manner.
In addition, in this method, the adhering amount is particularly irregular at the periphery, i.e., near the outer peripheral wall of the faceplate. This is considered attributable to the fact that the sliding movement of the phosphor particles is completely stopped or slowed down upon a direction change when a mass of phosphor particles collide against the outer peripheral wall. In any event, it is difficult to keep the attaching amount of phosphor particles constant over the entire inner surface of the faceplate and to obtain a phosphor screen without irregularly coated streak patterns. These problems are not encountered in the conventional slurry method.